This invention pertains to wireless telecommunications, and particularly to managing signaling when a wireless terminal is in a toggling or potential toggling scenario.
In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipment units (UE) such as mobile telephones (“cellular” telephones) and laptops with wireless capability (e.g., mobile termination), and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks is also called “NodeB” or “B node”. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions of the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a controller node, such as a base station controller (BSC) or radio network controller (RNC). The controller supervises and coordinates various activities of the plural base stations connected thereto. The controller nodes are typically connected to one or more core networks.
Different radio access networks (RAN) can have differing radio access technologies (RATs). One type of radio access technology (RAT) known as UTRAN is used by the Universal Mobile Telecommunications System (UMTS), a third generation mobile communication system which evolved from the Global System for Mobile Communications (GSM). UTRAN is a radio access network using wideband code division multiple access for user equipment units (UEs).
Another radio access technology (RAT) is known as GERAN, which is an abbreviation for GSM EDGE Radio Access Network. GERAN is a digital mobile phone technology that allows improved data transmission rates as an extension on top of standard GSM. GERAN is a part of GSM, and also of combined UMTS/GSM networks.
In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks, such as UTRAN and GERAN, and investigate enhanced data rate and radio capacity. The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies, resulting in yet further radio access technologies.
One of the further radio access technologies is the Evolved Universal Terrestrial Radio Access Network (EUTRAN). Another name for EUTRAN, is the Long Term Evolution (LTE) RAN. The core network where EUTRAN is connected to is called Evolved Packet Core (EPC), a.k.a. System Architecture Evolution (SAE) network. Both the EUTRAN and the EPC comprise together the Evolved Packet System (EPS) that is also known as the SAE/LTE network. A base station in this concept is called EUTRAN NodeB (eNodeB or eNB). In EUTRAN, the radio base station nodes (eNodeBs) are connected directly to a core network rather than to radio network controller (RNC) nodes, and the functions of a radio network controller (RNC) node are performed by the radio base stations nodes (eNodeBs). As such, the radio access network (RAN) of an EUTRAN/LTE system has an essentially “flat” architecture (comprising radio base station nodes without reporting to radio network controller (RNC) nodes). The evolved UTRAN thus comprises evolved base station nodes, e.g., evolved NodeBs or eNBs, providing evolved UTRA user-plane and control-plane protocol terminations toward the user equipment unit (UE). Moreover, in EUTRAN, the resources of communication systems, such as the frequency allocation and bandwidth are shared among multiple users simultaneously.
In many radio access technologies a wireless terminal, such as a user equipment unit (UE), can make transitions through several specified states, including a state known as Idle Mode and a state known as connected Mode. In Idle Mode the user equipment unit (UE) does not need to transmit or receive data, but can continue to scan the radio access network to keep track of its location and can receive pages. Also in Idle Mode the user equipment unit (UE) reports its location by sending updates to the network (such as Location Area Updates or Routing Area Updates in UTRAN, for example). When in the Idle Mode the user equipment unit (UE) is identified by identifiers such as the International Mobile Subscriber Identity (IMSI) and/or the Temporary Mobile Subscriber Identity (TMSI).
When a user equipment unit (UE) receives a confirmation about the establishment of a radio resource control (RRC) connection from the network, the user equipment unit (UE) goes into the connected mode. In the UTRAN-connected mode the user equipment unit (UE) is assigned a Radio Network Temporary Identity (RNTI).
As the user equipment unit (UE) can be mobile, the user equipment unit (UE) may wander or migrate from an area served by a radio access network (RAN) of a first type of radio access technology (RAT) to an area served by a network of another type of radio access technology (RAT). If the user equipment unit (UE) is capable of participating in communications with both types of radio access technologies (e.g., is a dual mode UE), and depending on various conditions, the user equipment unit (UE) may be handed over from the first radio access technology to the second radio access technology. In so doing, the user equipment unit (UE) can undergo an inter-RAT handover or participate in an inter-RAT cell reselection procedure.
At an access change to a new radio access technology (RAT), the user equipment unit (UE) typically engages in an area update procedure, e.g., a routing area update (RAU) in GERAN/UTRAN or a tracking area update (TAU) in EUTRAN. A tracking area comprises a cluster of eNodeBs (base station nodes) in the EUTRAN network. Each area update procedure involves signaling. For example, area update procedure signaling occurs when a user equipment unit (UE) transitions from a EUTRAN network to a GERAN/UTRAN network or vice versa.
On some occasions a user equipment unit (UE) may be situated or operated so as to experience repeated transitions back and forth between two radio access technologies. For example, as the user equipment unit (UE) travels it may “toggle” between the EUTRAN network and the GERAN/UTRAN network. Each toggle can potentially involve or invoke the signaling required for the area update procedure (e.g., RAU/TAU).
A concept known as Idle State Signalling Reduction (ISR) has been developed as an attempt to mitigate the amount of area update procedure signaling that could otherwise occur during toggling. In particular, the Idle State Signalling Reduction (ISR) is intended to reduce the frequency of TAU and RAU procedures caused by UEs reselecting cells between E-UTRAN and GERAN/UTRAN networks which are operated together. The Idle State Signalling Reduction (ISR) thus attempts to reduce the area update procedure signaling between the user equipment unit (UE) and the network, as well as the network internal signaling.
When the ISR feature is activated the user equipment unit (UE) is registered with nodes or entities which comprise or connect the respective radio access technologies with their core networks. That is, when the Idle State Signalling Reduction (ISR) feature is activates the user equipment unit (UE) is registered both with a core network node known as the Serving GPRS Support Node (SGSN) for the UTRAN and GERAN, and a core network node known as the Mobility Management Entity (MME) for the EUTRAN. The ISR feature is described, e.g., in 3GPP TS 23.401 V8.4.1. (2008-12), 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; General Packet Radio Service (GPRS) Enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Access (release 8), which is incorporated herein by reference in its entirety.
The Serving GPRS Support Node (SGSN) (for UTRAN and GERAN) is a signalling and in certain cases user plane entity serving the mobile stations within its geographical service area. Its tasks include mobility management (attach/detach and location management), logical link management, and authentication and charging functions, and for GERAN and optionally for UTRAN packet routing and transfer functions. The location register of the SGSN stores location information (e.g., current cell, current VLR) and user profiles (e.g., IMSI, address(es) used in the packet data network) of all GPRS users registered with this SGSN.
The Mobility Management Entity (MME) is a signaling entity in the core network (e.g., a core network node in some networks) for the EUTRAN. The main function of the MME is to manage the mobility of the user equipment unit (UE). As such, the MME is responsible for idle mode UE tracking and paging procedures including retransmissions. The MME is also responsible for authenticating the user.
When a UE attaches to a Mobility Management Entity (MME), it is allocated an identity, i.e. a GUTI (Globally Unique Temporary Identity). A GUTI consists of two parts, one part that identifies the MME which allocated the GUTI and which holds the UE context, and one part which identifies the UE within the MME. The part that identifies the MME is a Globally Unique MME Identity (GUMMEI), which in turn consists of a Public Land Mobile Network PLMN ID (i.e. MCC+MNC) [Mobile Country Code+Mobile Network code], an MME group identity (MMEGI) which identifies the MME pool and an MME code (MMEC) which identifies the MME within the pool. The part of the GUTI that identifies the UE within the MME is called M-TMSI (M-Temporary Mobile Subscriber Identity). The combination of MMEC and M-TMSI is denoted S-TMSI. The S-TMSI is used for identification of the UE in situations where the PLMN ID and MMEGI are known.
The Idle State Signalling Reduction (ISR) feature has thus been proposed to limit mobility related signaling during an inter-RAT cell reselection in idle state (ECM-IDLE state in E-UTRAN, PMM-IDLE state in UTRAN, GPRS STANDBY state in GERAN)). As mentioned above, with Idle State Signalling Reduction (ISR) the user equipment unit (UE) is registered in both the GERAN/UTRAN network and the EUTRAN network simultaneously, and does not perform an area update procedure (TAU/RAU) at access change once registered at both the SGSN and at the Mobility Management Entity (MME). When downlink data arrives to the user equipment unit (UE) in Idle Mode, paging is performed in both the GERAN/UTRAN network and the EUTRAN network. While the Idling State Signalling Reduction (ISR) feature is a very generic way of solving the toggling problem, Idle State Signalling Reduction (ISR) introduces significant additional complexity.